1. Field of the Invention
The present invention relates to an etching method applied to the formation of a fine circuit pattern or the like of a semiconductor device.
2. Description of the Related Art
As a conventional dry etching apparatus used in the formation of a fine circuit pattern or the like of a semiconductor device, for example, a cylindrical plasma etching apparatus, a microwave plasma etching apparatus, a parallel-plate reactive ion etching (RIE) apparatus are employed.
In recent years, a magnetron plasma etching apparatus in which a magnetron discharge is generated by a high-frequency electric field and a magnetic field perpendicular to the electric field to produce a plasma of a process gas was developed.
In the magnetron plasma etching apparatus, parallel-plate electrodes constituted by an upper electrode and a lower electrode which are opposite to each other are arranged in a vacuum chamber, and a semiconductor wafer serving as an object to be processed is mounted on the lower electrode. A high-frequency power is applied across the electrodes by a high-frequency power supply. A magnet is arranged above the vacuum chamber to generate a magnetic field perpendicular to the high-frequency electric field generated between the electrodes. The process gas is transformed into a plasma by a magnetron discharge caused by the above perpendicular electromagnetic field, and the semiconductor wafer is etched by the plasma.
In the above magnetron plasma etching apparatus, a plasma can be generated at a low pressure of, e.g., 100 mTorr or less, and a low-pressure process can be advantageously obtained.
When a silicon-containing layer such as a polysilicon layer is to be etched by using the magnetron plasma etching apparatus, a Cl.sub.2 or HCl gas is singly used as a conventional etching gas.
However, when the Cl.sub.2 gas or HCl gas is singly used as the conventional etching gas, and a polysilicon layer is to be etched by the magnetron plasma etching apparatus, etching of a pattern side portion caused by radicals, i.e., side etching occurs in a large quantity in a process in which the temperature of a semiconductor wafer is kept within a range of room temperature to about 100.degree. C., and anisotropic etching cannot be preferably performed.
For this reason, in a conventional technique, low-temperature etching in which a semiconductor wafer is cooled at a low temperature of, e.g., about -30.degree. C. to be etched is employed, thereby improving the anisotropy of etching.
However, the above low-temperature etching requires a coolant for cooling the semiconductor wafer, and an etching apparatus must have countermeasures against the low temperature, i.e., countermeasures against moisture condensation, thereby increasing the manufacturing cost of the semiconductor device.
In addition, after etching processing is performed by the above apparatus, since a semiconductor wafer cooled at a low temperature is conveyed from a vacuum chamber to a room set at the normal temperature, the Cl.sub.2 gas and the like adsorbed by the semiconductor wafer cooled at the low temperature are discharged into the room as the temperature of the semiconductor wafer is increased. The discharged gas may be hazardous to human bodies. Another problem is posed, i.e., moisture condensation occurs on the surface of the semiconductor wafer.